156 § 93. SPECIAL METHODS OF ANALYSIS. 



with water to the successive portions of which less and 

 less amnionic sulphide is added ; dissolve it in dilute hy- 

 drochloric acid, and add the solution to the first filtrate 

 from the stannic oxide, etc., containing the main part of 

 the alumina and ferric oxide. 



The solution obtained by treating the precipitated 

 stannic oxide and phosphate, etc., by ammonic sulphide, 

 contains all the phosphoric acid {Baehei\ Zeitschrift fur 

 die gesammten Naturwissenschaften^ 1864, 293. JFresenius' s 

 Zeitschrift^ 4, 122) / if its volume has been increased to a 

 considerable bulk by the washings of the precipitate of 

 aluminic hydrate and ferrous sulphide, concentrate it by 

 evaporation, filter again if not clear, and precipitate the 

 phosphoric acid with magnesia mixture in the usual man- 

 ner (§ 61, a). 



In the filtrate from the precipitated stannic oxide and 

 j)hosphate, etc., determine the bases, as directed in A, C, 

 and D, except that, since the precipitate by sodic acetate 

 in A contains no phosphoric acid, the difference between 

 the total weight of the precipitate by ammonia, and the 

 weight of the ferric oxide, as determined by potassic per- 

 manganate, gives the alumina. 



The method is not applicable in the presence of hydro- 

 chloric acid or chlorides. 



C. Precipitation of manganic hinoxide^ Mn 0„, in the 

 filtrate from the precipitate by sodic acetate hi A. 



Heat this filtrate, which should he free from ammonic 

 salts^ and tolerably concentrated, to 50 or 60° C, and con- 

 duct chlorine gas through it until it is saturated, or as long 

 as any precipitate is formed ; filter out the j^recipitate, add 

 more sodic acetate to the filtrate, pass clilorine through 

 again, and add this second precipitate to the first, if any 

 is obtained. Wash the precipitated manganic hydrate 

 first by decantation and then on the filter, dry this, sepa- 

 rate the precipitate from it as completely as possible, burn 

 it and dissolve the ash and the precipitate in concentrated 



